.a {
  width: 200px;
  height: 400px;
  padding: 11px;
  margin: 22px;
  background-color: lightblue;
  border: 3px solid red;
}

#a0 {
  /* 默认 content-box */
  box-sizing: content-box;
}

#a1 {
  /* borde-box 边框盒模型 */
  box-sizing: border-box;
}
